Electric fuse holder having a Hall-effect current sensor

ABSTRACT

A holder for an electric fuse is provided with a Hall-effect sensor arrangement which is integrally mounted in the fuse holder in close proximity to the current path through the holder. The Hall-effect sensor provides an output voltage responsive to the magnetic field resulting from the flow of current along the current path. The output from the Hall sensor is then processed to provide an indication of whether current is flowing through the fuse holder.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to fuse holders and moreparticularly to a fuse holder having a Hall-effect sensor which providesa signal responsive to the magnetic field present when current ispassing along the current path of the fuse holder.

2. Description of the Prior Art

As is well known, fuses for electric circuits are of numerous types andemploy a fusible element which is enclosed in a suitable housing suchas, for example, a cylinder of insulating material for preventing thecomponent parts of the protectors from damage or deterioration.Additionally, the fuse housings are constructed of various sizes andshapes to be readily received in or removed from receptacles provided inthe circuits with which the fuses are to be used.

When a large number of electrical circuits are provided in aninstallation, such as those in a large factory or on shipboard, it isextremely difficult for maintenance personnel to make the necessarytests of a number of fuses for the electric circuits before theparticular protector that has acted to open a circuit may be located.Such testing is an extremely time consuming operation and is more orless a hit-or-miss proposition.

Various attempts have been made in the past to develop fuses forelectric circuits which have indicators associated therewith in order toeliminate the necessity of manual inspection of the fuses. Some of thesehave been arranged to give an audible indication that a circuit hasopened while others have provided for a visual indication of such acondition. One prior and commonly used indicating arrangement forvisually showing that a fuse has blown and that a circuit is open hasbeen to arrange a lamp and series resistor in the circuit, across thefuse, in such a manner that when the fused circuit was operatingproperly, the lamp and resistor would be shorted out but in the eventthat the circuit was overloaded to the extent that the fuse interruptedthe circuit, a voltage would appear across the lamp to visually indicatethis condition. Such a resistor/lamp arrangement has proveddisadvantageous, for example, when the fuse blows, current will flowthrough the lamp and continue to flow through small load devices whichthe circuit is protecting, which may cause further breakdown in thecircuit or device. Another known prior arrangement is shown in U.S. Pat.No. 3,158,713 titled Apparatus for Indicating an Open Electrical Circuitwherein a solenoid is wired in parallel with the electrical fuse whichis actuated upon the fuse blowing to indicate that the fuse has operatedto protect the circuit.

Another approach to indicating that an electric fuse has opened toprotect an electrical circuit has been to provide an indicator in thefuse itself. Typically, such arrangements include a spring loaded pin orthe like which is released to a visually ascertainable position upon thefuse blowing to protect the circuit. Such fuses are considerably moreexpensive than fuses not having such indicators and such a feature isparticularly cost prohibitive in smaller low voltage class fuses.

SUMMARY OF THE INVENTION

In accordance with the present invention the holder or receptacle for anelectric circuit protector or fuse is provided with a Hall-effect sensorarrangement which is integrally mounted in the fuse holder in closeproximity to the current path through the holder. The Hall-effect sensorprovides an output voltage responsive to the magnetic field resultingfrom the flow of current along the current path. The output voltage fromthe Hall-effect sensor is then detected and electronically processed toprovide an indication of whether current is flowing through the fuseholder and the magnitude of such current flow.

In one embodiment means are provided for concentrating the magneticfield in the region of the Hall-effect sensor. The means forconcentrating also serves to support the Hall-effect sensor in thedesired location with respect to the current path.

According to a further embodiment a metal shield is provided to shieldthe input/output leads associated with the Hall-effect sensor from thecurrent path through the fuse base.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features that are considered characteristic of the inventionare set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of the preferredembodiments when read in connection with the accompanying drawingswherein like numbers have been employed in the different figures todenote the same parts and wherein:

FIG. 1 is a vertical elevation, partially broken away, of a fuse holderhaving a Hall-effect sensor arrangement;

FIG. 2 is a greatly enlarged detailed sectional view taken along theline 2--2 of FIG. 1;

FIG. 3 is a side view of the detailed showing of FIG. 2;

FIG. 4 is a longitudinal sectional view of one end of a fuse holdershowing one form of current sensor arrangement;

FIG. 5 is a sectional view taken along the line 5--5 of FIG. 4;

FIG. 6 is a view similar to FIG. 4 showing another form of sensorarrangement;

FIG. 7 is a sectional view taken along the line 7--7 of FIG. 6;

FIG. 8 is a view similar to FIG. 4 showing still another form of sensorarrangement;

FIG. 9 is a sectional view taken along the line 9--9 of FIG. 8;

FIG. 10 is a perspective view of a three phase fuse holder provided witha current sensor arrangement for each fuse;

FIG. 11 is a sectional end view taken along the line 11--11 of FIG. 10;

FIG. 12 is a circuit diagram of a fuse holder mounted current sensorarrangement for a three phase fuse holder.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Looking first at FIG. 1 reference numeral 10 refers generally to a fuseholder of the type conventionally used to receive a cartridge typeelectrical circuit protection device or fuse 12. The fuse includes acylindrical insulating body 14 and a pair of end caps 16, 18 definingspaced electrical terminals at the opposite ends thereof.

The fuse holder comprises a mounting base 20 formed from a suitabledielectric material such as, for example, being molded from athermosetting phenolic compound. Attached to the upper surface 22 of thefuse base are a pair of spaced apart fuse engaging clips 24,26. Theclips are suitably attached to the upper surface 22 at locations suchthat they may be electrically conductively engaged with the spaced apartterminals 16, 18 of a fuse adapted to be mounted in the base. Each ofthe fuse clip elements 24, 26 has associated therewith an electricalconnector each of which is electrically conductively attached to itsassociated fuse clip 24, 26, respectively. The connectors 28, 30 eachserve to electrically cooperate with external conductors (not shown)thereby defining the path followed by electric current through the fusebase.

In the embodiment shown in FIG. 1 each of the fuse clip/connectorarrangements is of the type having a spring type fuse clip adapted topositively engage one of the cylindrical end caps of a fuse and a "boxtype" connector for providing the connection to the external wiring.While not shown specifically in the drawings it should be appreciatedthat each of the "box type" connectors is provided with a throughopening extending horizontially therethrough as viewed in FIG. 1 toreceive the bare end of a wire, the wire is then positively retained inthe connector by engagement with the vertically extending set screws 32,34 as shown in the drawing figure.

Looking now specifically to the clip/connector arrangement 26/30 on theright hand side of the fuse holder of FIG. 1 it will be seen that theconnector 30 and the fuse clip 26 are electrically interconnected by aflat section 36 of electrically conductive material providing thecurrent path between the connector and the fuse clip. All metallic partsin such fuse holders are typically made of very high quality electricalcopper and bronzes depending on the requirements of the particular fuseholder and in many cases may be provided with a protective plating onthe outer surface thereof.

The flat conductive interconnecting portion 36 defined above lies insubstantially direct contact with the upper surface 22 of the fuseholder base 20. It will be seen with reference to FIGS. 1, 2, and 3 thatthe fuse holder base, in the region of the interconnecting strip 36,comprises a wall 37 of insulating material defining a substantially flatdownwardly facing lower surface 38 which is substantially parallel tothe upwardly facing surface 22 with which the interconnecting strip 36is in confronting relation. It has been found that, when current isflowing through the fuse holder, the flow of current through theinterconnecting strip 36 results in a particularly useful magnetic fieldtherearound which may be sensed by a current sensing device positionedadjacent the downwardly facing surface 38 of the fuse base describedabove.

In the embodiment shown in FIG. 1, 2, and 3 the current sensor 40comprises a Hall-effect device which is capable of providing an outputvoltage which is directly proportional to current flow through the flatinterconnecting section 36. The specifics of the arrangement of thiscurrent sensor device and the novel aspects thereof as shown in FIG. 1,2, and 3 will be further described in greater detail hereinbelow.

It should be appreciated that in its broadest sense the inventioncomprises the incorporation in a fuse holder of a current sensing devicecapable of detecting the flow of current through some portion of thecurrent path of the fuse holder. With that in mind reference is madeagain to FIG. 1 wherein it will be appreciated that the current paththrough such a fuse holder begins at the right hand end of the fuseholder with the first connector 30 adapted to engage an external powersource and from there it extends through the interconnecting element 36to the first fuse clip 26. From the fuse clip 26 the current pathextends through the right hand fuse cap 18, through the fusible elementof the fuse contained within the fuse casing to the left hand fuse cap16. From the left hand fuse cap 16 the current path extends through theleft hand clip 24 through the left hand interconnecting strip 27 and tothe left hand connector block 28 for engaging a second externalconductor. According to the invention, current sensor means may beincorporated within a fuse holder anywhere along the "current path" ofthe fuse holder wherein sufficient magnetic flux is present, as a resultof the flow of current through the fuse holder, to permit sensing of themagnetic field. One particularly advantangeous way of sensing thepresence of such magnetic field is a sensor of the type which may bebroadly categorized as an "inductive type pick-up arrangement". In itsbroadest sense such an inductive pick-up arrangement may comprise, byway of examples: a conductive wire extending parallel to the currentpath through the fuse holder; a rod of ferromagnetic material positionedin the mounting base in close proximity to the current path; or, a coilof wire such as for example a coil of enameled copper wire. Any of theabove described simple inductive pick-up means is capable of having acurrent induced therein as a result of interaction with the magneticfield which is present along the current path through the fuse holder.Such induced current results in a useful signal which may then beprocessed to derive information relating to the current flow through thefuse holder.

More specifically the signal or output voltage from the current sensingdevice may be detected and processed by a variety ofelectrical/electronic means to provide an indication of whether currentis flowing through a fuse holder and the magnitude of such current flow.

In one simple embodiment the output voltage from a fuse holder mountedcurrent sensor has been used to power a visually ascertainable indicatormounted directly on the fuse holder base, such as an L.E.D. or an L.C.D.

It should be appreciated that while the invention, for matter ofconvenience, is described in connection with a fuse holder of the typeadapted to carry a cartridge type fuse the invention may be applied toany fuse holder type. More specifically, it should be appriciated that,any fuse holder has a "current path" therethrough and the presentinvention is intended to include the incorporation of a current sensorin other types of fuse holders along such current path at a locationwherein sufficient magnetic flux is present to enable interaction of acurrent sensor with the magnetic field surrounding a portion of thecurrent path when current is passing through the fuse holder/fusecombination.

Looking now to FIGS. 4 and 5 a current sensor 42 making use of theinductive pick-up principle is illustrated wherein a coil 44 ispositioned in the region underlying the fuse base upper surface 43 whereit will be electromagnetically coupled with the magnetic field of thefuse base. In this embodiment the fuse holder base 46 is show in asomewhat simplifed form from that of FIG. 1. The connector arrangement48 for electrically cooperating with an external conductor is also shownin a simplified form. As with the embodiment of FIG. 1 the currentsensor 42 is positioned adjacent the downwardly facing surface 50 of thetop wall of the fuse holder mounting base in a position in closeproximity to a flat conductive strip 52 interconnecting the connector 48and one of the fuse clips 54. In the embodiment in FIGS. 4 and 5 thecurrent sensor 42 comprises a bobbin 56 having a longitudinallyextending opening therethrough through which an iron core 58 is suitablypositioned and retained. The bobbin 56 is wound with a coil 44 thereupondefined by a plurality of circumfrential windings of a suitable enameledcopper wire or the like. The number of windings defining the coil isdependent on the amperage rating of the fuse holder in which the coil isincorporated, a larger number of windings being necessary on loweramperage rating fuse holders in order to obtain the necessary outputacross the coil. As shown in FIG. 4 and 5 the ends 60 of the coil areelectrically connected with a suitable output connector 62 so that thesignal induced across the output of the coil as a result of theelectromagnetic coupling with the current through the fuse base may bereadily accessed by whatever signal processing equipment the end userdeems appropriate for his application.

Looking now at FIGS. 6 and 7 a modification of the current sensorarrangement of FIGS. 4 and 5 is shown. In this embodiment an opening 64is provided in the top supporting wall 63 of the fuse base. The opening64 passes from the upward surface 66 upon which the fuse clip 68 andconnector 70 are mounted, through and into communication with the regionunderlying and adjacent the downwardly facing surface 72 of the wall 63.The flat section of electrically conductive material 74 whichinterconnects the fuse clip 68 and the connector 70 passses downwardlythrough the above described opening 64 and forms a loop 76 in the regionadjacent the downwardly facing surface 72 and then passes upwardly againthrough the opening 64 back to a position adjacent to the upwardlyfacing surface 66. Passing through the loop 76 defined by the currentcarrying interconnecting member is a current sensing arrangement 78comprising a bobbin 80, iron core 82, and winding 84 of the typedescribed hereinabove with respect to FIGS. 4 and 5. The loop 76 formedby the current carrying interconnecting member 74 around thebobbin/coil/core arrangement serves to concentrate the magnetic fluxpassing through the interconnecting member 74 in a manner enabling thearrangement to sense smaller currents passing along the current paththan possible with the embodiment of FIGS. 4 and 5.

In this embodiment the coil output leads 61 are connected directly to anindicator, comprising for example an L.C.D. or an L.E.D. 65 which ismounted directly on a side wall 67 of the base of the fuse holder. Thisindicator 65 provides a visually ascertainable display, carried directlyby the fuse holder, responsive to the electric signal generated by thecurrent sensor 78.

Looking now to FIGS. 8 and 9 another inductive type current sensorarrangement 86 is shown. As in the embodiment of FIG. 6 & 7, the currentcarrying member 88, which interconnects the fuse clip 90 and theexternal connector 92, passes from the upper surface 94 of the fuse base96 through an opening 98 therein to form a loop 100 adjacent thedownwardly facing lower surface 102 of the support wall of the fuseholder. This embodiment is essentially a current transformer, in that acore 104 formed from a suitable ferromagnetic material such as ironpasses through and encircles the loop 100 formed by the interconnectingmember 88. A portion 106 of the iron core 104, not lying within theloop, is provided with a suitable winding 108 of conductive wire whichforms the secondary winding of the current transformer. The loop 100formed by the interconnecting member 88 serves as the primary winding ofthe current transformer. As in the embodiment of FIGS. 4 and 5 the endsof the secondary winding 108 across which a useful signal is generatedmay be attached to a suitable output connector 110 to provide access bythe end user. Alternatively a direct indicating arrangement as shown inFIGS. 6 and 7 may be used.

Returning now to FIGS. 1 through 3, in the embodiment shown, theHall-effect sensor 40 is actually a magnetically responsive device whichutilizes the Hall-effect for sensing a magnetic field. Specifically, aHall cell included in the device senses a magnetic field and provides anelectrical output corresponding to the presence or absence of a magneticfield. Such a Hall-effect device is the Sprague UGN-3503U, which inaddition to the Hall cell, includes an amplifier, trigger, and outputstages integrated into a single monolithic chip.

One of the advantages of this Hall-effect device is that it has anextremely small outer package dimension which facilitates positioning ofthe device in a variety of fuse holder configurations, particularly,smaller fuse holders having limited space available for mounting of acurrent sensing device.

The Hall-effect device itself 40 is square and substantially flat andhas three in-line pins providing input and output connections. One ofthe outer pins 112 is connected to a regulated DC power supply toprovide a collector voltage to the output transistor of the Hall-effectdevice. The other of the outside pins 114 is the output pin at which the"Hall-voltage" is present when current is flowing through the fuseholder. The center pin 116 is a common ground for both the input voltageand the output or Hall voltage.

The Hall-effect device 40 is supported in the desired positionunderlying the downwardly facing surface 38 of the wall 37 of the fuseholder base in close proximity to the current carrying, interconnectingstrip 36 by a pair of L-shaped brackets 118. One leg 120 of each of theL-shapped brackets 118 is fixedly attached to the downwardly facingsurface 38 of the wall 37 by suitable means such as for example acyanoacrylate adhesive. The L-shaped brackets 118 are positioned so thatthe other legs 122 of the brackets extend downwardly from the surface 38with the opposing faces 124 of the legs defining an air gap 126therebetween. The air gap 126 is substantially the same thickness as thenarrow dimensions of the Hall-effect device 40 and the device isadhesively attached to the faces 124 to retain it in the desiredlocation within the air-gap.

It should be appreciated that the position of the Hall-effect device 40with respect to the interconnecting strip 36 may be easily controlled byselective positioning of the Hall-effect device 40 in the air gap 126defined by the L-shaped brackets.

L-shaped brackets 118 are each fabricated from a ferromagnetic materialwhich is capable of concentrating the magnetic field which surrounds theinterconnecting strip 36, when current is flowing through the strip,into the air gap 126 and therefore in the region of the Hall-effectsensor 40.

Looking now at FIG. 1 the fuse holder mounting base 20 is shown sittingupon a rectangular metal box 128 comprising four side walls 130 and anupper wall 132. The four side walls 130 are substantially coextensivewith the outer perimeter of the fuse holder mounting base 20 and theupper wall 132 interconnecting the upper edges of the four side walls iscoextensive with the downwardly facing surface of the fuse base. A smallopening 134 is provided in the upper wall 132 of the metal box 128through which the three leads 136 associated with the Hall-effect sensormeans 40 pass to their appropriate input/output terminals. The terminals138 associated with the three outputs are located in one of the sidewalls 130 of the metal box and are indicated symbolically by a circle,triangle, and square in FIG. 1.

The metal box 128 described hereinabove is made from a material whichserves to shield the conductors 136 associated with the Hall-effectsensor 40 from the current path of the fuse holder. Accordingly, whilethe magnetic field surrounding a portion of the current path of the fuseholder is of the utmost importance to the sensing arrangement of thepresent invention it is desired to shield the inputs and outputs to thesensing means 40 from this magnetic field in order to avoid interferenceand crosstalk between the circuits.

Looking now to FIGS. 10 and 11 a three pole fuse holder 140 is shownwhich may be readily used to protect a three phase electrical supplysystem. Each of the three fuse holders 142 shown in these figures issubstantially the same as that illustrated in FIG. 1. More specifically,each is supplied with its own current sensor arrangement 144 comprisinga Hall-effect sensor 146 mounted to the downwardly facing surface 148 ofthe fuse holder base 150 by a magnetic field concentrating arrangement152 as described in detail hereinabove. The three pole fuse holder 140is mounted upon a rectangular shielding box 154 provided with threeopenings 156 in the top wall 158 thereof to permit passage into the boxof the input/output leads 160 associated with the three separateHall-effect current sensing arrangements 144. After passing throughtheir respective openings 156 into the shielded box 154 all of theinput/output leads 160 pass to a suitable access panel 162 on one side164 of the shield box 154. At the access panel 162 the inputs andoutputs are identified as to which of the three fuse holders 142 theyare associated with by an appropriate numbering or color-coded scheme.As shown in FIG. 10 a symbol system, as described above, may be used toidentify the pin connection with which the connectors are associated.

FIG. 12 is a circuit diagram of the invention as applied to a threephase fuse holder such as that shown in FIGS. 10 and 11. A three phasepower source, "Line" 168, is applied to a three phase load 170 by threebus bars 172. A three phase fuse holder of the type shown in FIG. 10 and11 which is represented generally by the dashed outline 174 isinterposed between the power source 168 and load 170. The fuses,protecting the three phases are identified by the reference numerals176, 178, and 180, and the portion of the current path of the three fuseholders to be sensed by the current sensors are identified respectivelyby the reference numerals 182, 184, and 186. Current sensors, eachidentified by the reference numeral 188, comprising Hall-effect devices,are positioned adjacent each of the portions of the fuse holder currentpaths to be monitored. As discussed hereinabove each of the Hall-effectsensors has three leads associated with it. A first lead 190 providingan input voltage from a 5 volt regulated DC power supply, a second 192providing the output for the Hall voltage, and a third lead 194comprising a common ground for both input and output circuits.

The output 192 from the three current sensing arrangements 188 is shownpassing into a box 196 identified in the drawing as a signal conditionerwherein suitable well known electronic signal conditioning means may beemployed to amplify and process the output signals and to generateappropriate outputs 198 for monitoring the condition of the threecircuits. The monitor may comprise a visual display such as an L.E.D. orthe like or, more sophisticated electronic circuitry may be used toderive further information from the output.

This invention may be practiced or embodied in still other ways notdeparting from the spirit or essential charactor thereof. The preferredembodiments described herein are therefore illustrative and notrestrictive, the scope of the ivention being indicated by the appendedclaims and all variations which come within the meaning of the claimsare intended to be embraced therein.

What is claimed is:
 1. A holder for an electric fuse, the fuse having apair of spaced electrical terminals, the holder comprising:a mountingbase formed from a dielectric material; first means, carried by saidbase, for electrically conductively cooperating with one of the fuseselectrical terminals and for electrically conductively cooperating witha first external conductor; second means, carried by said base, forelectrically conductively cooperating with the other of the fuseselectrical terminals and for electrically conductively cooperating witha second external conductor; said first means and said second meanstogether defining the current path through said fuse holder when anelectric fuse is in cooperating relationship therewith; and, Hall-effectsensor means carried by said mounting base in close proximity to aportion of said current path, providing an output voltage responsive tothe magnetic field resulting from the flow of current along said currentpath.
 2. The fuse holder of claim 1 wherein said mounting base comprisesan upper surface and a lower surface, said first means and said secondmeans which define the current path through said fuse holder beingmounted on said upper surface of said mounting base and wherein saidHall-effect sensor means is positioned adjacent to said lower surfacethereof at a location in close proximity to said current path.
 3. Thefuse holder of claim 1 including means affixed to said base forconcentrating the magnetic field in the region of said Hall-effectsensor.
 4. The fuse holder of claim 3 wherein said means forconcentrating also supports said Hall-effect sensor in a predeterminedlocation with respect to said current path.
 5. The fuse holder of claim2 including means for concentrating the magnetic field in the region ofsaid Hall-effect sensor.
 6. The fuse holder of claim 5 wherein saidmeans for concentrating comprises a pair of substantially L-shapedferromagnetic elements, each comprising two legs, one leg of each ofsaid L-shaped elements being affixed to said lower surface of said base,the other legs of said L-shaped elements being in confrontingrelationship with one another to define an air gap there betweenunderlying said lower surface and in close proximity to said currentpath;said Hall-effect sensor being fixedly supported in said air gap ata predetermined position with respect to said current path by said otherlegs.
 7. A holder for an electric fuse, the fuse having a pair of spacedelectrical terminals, the holder comprising:a mounting base formed froma dielectric material; a fuse clip mounted on said base for electricallyconductively cooperating with one of the fuses electrical terminals; aconnector means mounted on said base for electrically conductivelycooperating with a first external conductor; means for electricallyinterconnecting said fuse clip and said connector means; means, carriedby said base, for electrically conductively cooperating with the otherof the fuses terminals and for electrically cooperating with a secondexternal conductor; and, Hall-effect sensor means carried by saidmounting base in close proximity to said means for electricallyinterconnecting said fuse clip and said connector means, for providingan output voltage responsive to the magnetic field resulting from theflow of current through said means for interconnecting.
 8. The fuseholder of claim 7 wherein said mounting base comprises an upper surfaceand a lower surface, said fuse clip, said connector means, said meansfor electrically interconnecting, and said means for electricallyconductively cooperating are all mounted on said upper surface of saidmounting base, and, wherein, said Hall-effect sensor means is affixed tosaid mounting base adjacent to said lower surface thereof at a locationin close proximity to said means for electrically interconnecting saidfuse clip and said connector means.
 9. The fuse holder of claim 7including means for concentrating the magnetic field in the region ofsaid Hall-effect sensor and for supporting said Hall-effect sensor in apredetermined location with respect to said means for interconnecting.10. The fuse holder of claim 2 wherein said Hall-effect sensor meansincludes a plurality of electrical leads associated therewith andwherein a metal shield means is mounted to said mounting base adjacentto said lower surface thereof and is provided with an opening therein inclose proximity to said Hall-effect sensor whereby said conductors arepassed through said opening and are shielded from said fuse holderscurrent path by said shielding means.